1. Field of the Invention
The present invention relates to a motor driving control device that controls the driving of a motor, and more particularly to a motor driving control device that drives and controls the motor without the use of a magnetic-pole position sensor.
2. Description of Related Art
There have conventionally been developed techniques for detecting the magnetic-pole position of a rotor of a motor without the use of a sensor. Some of such techniques propose to detect the polarity or the position of the magnetic pole of the rotor by exploiting injection of a high-frequency rotation voltage or a high-frequency rotation current.
With reference to FIGS. 41 and 42, a polarity checking technique for a permanent-magnet synchronous motor will be described. Checking of the polarity is performed by exploiting the fact that magnetic saturation of the stator core exhibits anisotropy depending on the rotor direction. FIG. 41 is a conceptual diagram of the magnetic flux when the magnetic flux of the stator and the magnetic flux (d axis) of the rotor are pointing in the same direction, and FIG. 42 is a conceptual diagram of the magnetic flux when the magnetic flux of the stator and the magnetic flux (d axis) of the rotor are facing away from each other.
When the magnetic flux (the magnetic flux of the stator) produced by the passage of a current through an armature winding provided in the stator is pointing in the same direction as the magnetic flux (the magnetic flux of the rotor) produced by the permanent magnet provided in the rotor, the sum of the magnetic flux becomes relatively large, whereby magnetic saturation easily occurs. On the other hand, when the magnetic flux of the stator and the magnetic flux of the rotor are not pointing in the same direction, the sum of the magnetic flux becomes relatively small, whereby magnetic saturation hardly occurs.
When magnetic saturation occurs, the inductance of the motor is decreased, and the current becomes relatively high. As a result, when a voltage with which magnetic saturation occurs is applied to the motor in such a way that the stator produces the magnetic flux in the direction of the d axis (see FIG. 41), the winding current becomes greater than when the voltage is applied in such a way that the stator produces the magnetic flux in the opposite direction (see FIG. 42). By exploiting such characteristics, the direction of the d axis, i.e. the polarity of the magnetic pole of the rotor can be checked by applying, in the respective positive and negative directions of the d axis, a voltage with which magnetic saturation occurs.
Generally, estimation of the magnetic-pole position is performed by estimating the inclination of the d axis. However, such an estimation technique cannot be applied to estimation of the direction of the d axis (i.e. it is impossible to estimate whether the direction of the d axis lies within the range from 0 to π or within the range from π to 2π in electrical angle). Thus, checking of the polarity is performed after estimation of the magnetic-pole position, thereby estimating the magnetic-pole position within the range from 0 to 2π as well as the direction of the d axis.
JP-B-3381408 (hereinafter refereed to as “Patent Document 1”), JP-A-2003-189673 (hereinafter referred to as “Patent Document 2”), JP-A-2003-219682 (hereinafter referred to as “Patent Document 3”), or the like disclose a technique according to which checking of the polarity is performed. With a configuration disclosed in Patent Document 1, a voltage with which a magnetic saturation current is generated is applied between predetermined phases once while the rotor is at standstill so as to perform checking of the polarity. With a configuration disclosed in Patent Document 2, an alternating voltage is applied only to the d axis (γ axis), so that checking of the polarity is performed based on the d-axis (γ-axis) current locus. With a configuration disclosed in Patent Document 3, the voltage vector is made to rotate, so that checking of the polarity is performed based on the magnitude of the current vector of the current locus in the major-axis direction.
FIG. 43 shows a configuration block diagram of a typical conventional motor drive system, which is shared by the techniques disclosed in the Patent Documents described above. In FIG. 44, the waveform of the γ-axis current (the d axis current estimated for the purpose of control) iγ used for checking of the polarity is shown. The γ-axis current iγ is fed to a polarity checker 120 shown in FIG. 43, and a high-frequency voltage is applied to a motor. If the positive amplitude of the γ-axis current iγ is found to be larger than the negative amplitude thereof, the polarity checker 120 judges that the polarity is appropriate; if the positive amplitude of the γ-axis current iγ is found to be smaller than the negative amplitude thereof, the polarity checker 120 judges that the polarity is inverted. Then the estimated magnetic-pole position is corrected according to the judgment results.
However, in the conventional technique typified by the configuration shown in FIG. 43, as a result of checking of the polarity being performed by using the difference between the positive and negative amplitudes of the γ-axis current iγ including a direct-current component (and a low-frequency component that can be regarded as a direct-current component), the following problems arise. The influence of the offset of the current sensor is emphasized, and susceptibility to the influence of a drive current or an induction voltage (in other words, electromotive force) is increased when the motor is driven (rotated) or is running freely. In other words, these influences make it impossible to perform checking of the polarity correctly. In addition, to weaken these influences, it is necessary to pass a relatively high current. It should be noted that, since the frequency of the high-frequency voltages vhγ* and vhδ* to be superposed for performing checking of the polarity are sufficiently higher than that of the drive current or the like, the frequency of the drive current or the induction voltage as obtained when the motor is driven (rotated) or is running freely can be regarded as being (substantially) a direct-current component with respect to the frequency of the high-frequency voltage used for performing checking of the polarity.
Likewise, also in a case where the magnetic-pole position is estimated by using the high-frequency rotation voltage or the like, development of the method that is less susceptible to the influences of the offset, drive current, and induction voltage described above is keenly sought after.